[G_Rossney]

Originally Posted by FR-S2GT86

There's ALWAYS only been one feed for the dash and door speakers.

You, yourself said further up this thread that you ".....know less than nothing about modern car sound systems....." You still have both mid-range speakers and tweeters in the dash, right?

Trust me on this, the wiring in the car hasn't changed. There is still a full-range signal sent from the head unit to the amp in back since your door speakers are still operating.....only now, since there is a bypass harness connected, they're running at full-range instead of through the low-pass filtering inside your amp as the system was designed originally.

Removing the bypass plug and reconnecting it to the factory amp will NOT amplify your dash speakers as you suspect they will, since those dash speakers are on the SIGNAL side of the amp, not the SPEAKER OUTPUT side. I installed car audio and other mobile electronics professionally back in the late 90's and am now getting back into it with my new build on this current car, and have gotten to know it pretty well. Trust me. It won't hurt to try this simple experiment:

1) Remove the bypass plug at the factory amp location, plug the harness back into your factory amp.

2) Reinstall the fuse that was pulled out in the fuse panel that was removed when the new "upgraded" head unit was installed by the dealer.

3) Jumper the +12 volt amp power supply lead (which now has +12 volts on it there at the amp harness which was non-existent previously due to the fuse being removed) to the amplifier turn-on lead to get the amp to turn on.

4) Turn on your head unit and take a listen.

You should now have a full range signal input to the factory amp again and a low-pass filtered speaker output to your doors.

Let us know how it sounds.

I'm trying to get a 2019/2020 Navi/Android Auto HU to work in my 2013 BRZ. I've got all functions working except that door speakers (no low end/bass). I figured the AMP lead from the HU is not making it to the AMP. I thought just getting the AMP powered would solve the issue, but I've searched the wiring diagrams and can't seem to find the wiring diagram for the amp to determine which lead is the lead to turn it on. Is it as simple as a 12v power supply??